Sensitive Oxidation State Ambivalence in Unsymmetrical Three-Center (M/Q/M) Systems (acac)2Ru(m-Q)Ru(acac)2n, Q = 1,10-Phenanthroline-5,6-dione or 1,10-Phenanthroline-5,6-diimine (n = +, 0, -, 2-)
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Inorganic Chemistry 44 (9): 3210--3214 (2005)

The new redox systems (acac)2Ru(m-Q1)Ru(acac)2n (1n) and (acac)2Ru(m-Q2)Ru(acac)2n (2n) with Q1 = 1,10-phenanthroline-5,6-dione and Q2 = 1,10-phenanthroline-5,6-diimine were studied for n = +, 0, -, and 2- using UV-visible-NIR spectroelectrochem. and, in part, EPR and susceptometry. The ligands can bind the first metal (left) through the phenanthroline N atoms and the second metal (right) at the o-quinonoid chelate site. The neutral compds. are already different: Compd. 1 is formulated as a RuII(m-Q1).bul.-RuIII species with partially coupled semiquinone and Ru(III) centers. In contrast, a RuIII(m-Q2)2-RuIII structure is assigned to 2, which shows a weak antiferromagnetic spin-spin interaction (J = -1.14 cm-1) and displays an intense half-field signal in the EPR spectrum. The 1-electron reduced forms are also differently formulated as RuII(m-Q1)2-RuIII for 1- with a RuIII-typical EPR response and as RuII(m-Q2).bul.-RuII for 2- with a radical-type EPR signal at g = 2.0020. In contrast, both 12- and 22- can only be described as RuII(m-Q)2-RuII species. The monooxidized forms 1+ and 2+ show very similar spectroscopy, including a RuIII-type EPR signal. Although no unambiguous assignment was possible here for the alternatives RuII(m-Q)0RuIII, RuIII(m-Q)2-RuIV or RuIII(m-Q).bul.-RuIII, the last description is favored. The reasons for identical or different oxidn. state combinations are discussed. on SciFinder(R)
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